I currently own a home that has 1400 sq feet in the main part of the house. It has an addition on the back with a finished basement which has 900 sq ft upstairs and including the basement. The main part of the house has a Trane XL90(85,000) btu gas furnace with an trane XL1200 2 ton condenser. The addition has a 10-13 year old carrier 75,000 btu furnace with a trane XL1200 1.5 ton condenser. well I am adding on to make way for a fourth child. We are adding a small bedroom and pantry and an attached two and a half car garage. The old garage which is 22 X 22 will be converted into a new family room (slightly vaulted ceiling). The old family room will be a dining room. I won't be heating or cooling the garage portion of the addition. However the bedroom (10 X 17) and pantry (10 X 10) will need HVAC as well as the new family room (22 X 22). The reason I am not replacing the Trane HVAC units is because they are only six years old. So finally to the question at hand. I am looking at a new heat pump for the new addition. Is there a general rule of thumb on SEER as far as bang for buck? I mean is a 16 SEER unit going to save me 50% more than a 14 SEER on heating and cooling costs? I have been looking at Trane and Carrier (I kinda figured since this is what I currently own). Is there a way to say you need 1 ton of cooling capacity for every 600 sq ft of living space? Oh yeah, the new addition is on concrete no crawl space. I hope this is enough info for an informed decision. I am also taking into account any rebates/financing by either manufacturer and at least a ten year warrenty on parts and labor. Again I am trying to consider ALL factors. I would prefer to go to a variable speed if the cost isn't out of this world. When I bought the Tranes six years ago the variable speed was double. Thanks for your help and consideration guys. Charles Abbott. One last thing this summer I had a dead short in the smaller condenser outside. HVAC contractor came over and I helped him take the cover off. The problem was some sort of heater mounted on or very near the compressor. The wire feeding this heater had been too close to the compressor, heated the insulation around them and shorted out. He replaced the burned wiring only I wonder if the entire heater should be replaced? It is under warrenty and I asked he said I didn't have to have it for the unit to work however I figured since the manufacturer designed it to be in there. Well the unit works but how do I know if the heater is working or not? Should I have another Trane dealer look at it? Just curious? Thanks again Charles.